.\" Copyright (c) 2008 Cisco Systems.  All rights reserved.
.\"    Author: Julian Elischer
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.Dd January 10, 2025
.Dt SETFIB 2
.Os
.Sh NAME
.Nm setfib
.Nd set the default FIB (routing table) for the calling process
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/socket.h
.Ft int
.Fn setfib "int fib"
.Sh DESCRIPTION
The
.Fn setfib
system call sets the associated FIB (routing table) for all sockets opened
subsequent to the call, to be that of the argument
.Fa fib .
The
.Fa fib
argument
must be greater than or equal to 0
and less than the current system maximum which
may be retrieved by the
.Va net.fibs
sysctl.
The system maximum is set in the kernel configuration file with
.Bd -ragged -offset indent
.Cd "options ROUTETABLES=" Ns Em N
.Ed
.Pp
or in
.Pa /boot/loader.conf
or
.Pa /etc/sysctl.conf
with
.Pp
.Dl net.fibs= Ns Qq Em N
.Pp
where
.Em N
is an integer smaller than 65536.
Note that the number of FIBs may be increased after booting, but cannot be
reduced.
.Pp
The maximum of 65536 is due to the implementation storing
the FIB number in a 16-bit field in the
.Xr mbuf 9
packet header, however it is not suggested that one use such a large number
as memory is allocated for every FIB regardless of whether it is used, and
there are places where all FIBs are iterated over.
.Pp
The default FIB of the process will be applied to all protocol families
that support multiple FIBs, and ignored by those that do not.
The default FIB for a process may be overridden for a socket with the use
of the
.Dv SO_SETFIB
socket option.
.Sh RETURN VALUES
.Rv -std setfib
.Sh ERRORS
The
.Fn setfib
system call
will fail and no action will be taken and return
.Er EINVAL
if the
.Fa fib
argument is greater than the current system maximum.
.Sh SEE ALSO
.Xr setfib 1 ,
.Xr setsockopt 2
.Sh STANDARDS
The
.Fn setfib
system call is a
.Fx
extension however similar extensions
have been added to many other
.Ux
style kernels.
.Sh HISTORY
The
.Fn setfib
function appeared in
.Fx 7.1 .
